A rechargeable secondary electric cell (i.e. a battery) is mounted in a portable electronic equipment such as a mobile communication terminal, a PDA and so on. To charge the secondary electric cell (i.e. battery), it requires a separate power supply for supplying electric energy to the battery of the portable electronic equipment using a commercial power source for domestic use. Typically, each of the power supply and the battery has a separate external contact terminal, and thus the power supply is electrically connected to the battery by connecting to the two contact terminals.
However, if the contact terminals protrude outward, this leads to bad appearance and the contact terminals are contaminated by external impurities, resulting in poor contact state. And, if the battery is disconnected or exposed to moisture due to a user's carelessness, the battery is apt to lose the charging energy.
To solve a contact-type charging method, a wireless charger system has been suggested, which charges a power supply and a battery in a contact-less manner.
Prior arts teach contact-less charger systems, which charge a battery using inductive coupling between a primary coil of a charging body and a secondary coil of a battery pack without contact terminals, as disclosed in Korean Laid-open Patent Publication No. 2002-57468, Korean Laid-open Patent Publication No. 2002-57469, Korean Patent Registration No. 363,439, Korean Patent Registration No. 428,713, Korean Laid-open Patent Publication No. 2002-35242, Korean Utility Model Registration No. 217,303, U.K. Laid-open Patent Publication No. 2314470, U.S. Laid-open Patent Publication No. 2003/0210106, Japanese Laid-open Patent Publication No. 2002-209344, Japanese Laid-open Patent Publication H9-233706, Japanese Laid-open Patent Publication No. 2001-258182, and U.S. Pat. No. 6,316,909.
However, the above-mentioned conventional contact-less charger systems have a disadvantage that the charging efficiency depends on the positional relationship between the primary coil and the secondary coil. That is, in case positional offset exists between the primary coil and the secondary coil, induced electromotive force is insufficiently induced to the secondary coil, and thus the contact-less charger system has lower charging efficiency than a contact-type charger system. Therefore, the user should arrange the portable electronic equipment or the battery pack having the secondary coil therein at an optimal position on the charging body.
To solve the problem, attempts have been made to change the arrangement pattern of the primary coil for securing high charging efficiency regardless of location or orientation of the secondary coil.
Korean Patent Registration No. 524,254 (hereinafter referred to as 254' patent) discloses a contact-less charger system, in which a flat core is formed by connecting a plurality of small-sized cores made of cobalt-based or ferrite materials, and a core block is formed by winding a predetermined pattern of coil on the flat core and mounted in a wireless charging pad (a primary charging body).
The above 254' patent arranges a plurality of coils alternately or parallel on the same plane of the charging body to compensate for positional offset between a primary coil and a secondary coil, which results in excessive waste of energy, compared with a contact-less charger system using a single coil.